Truck platooning uses autonomous and connected vehicle capabilities to enable two or more semis to travel in sequence at a close, constant distance. The lead and follower vehicles are tethered via vehicle-to-vehicle communications, maintaining a steady gap of as little as 30 feet at highway speeds. Speed, acceleration and braking are monitored and precisely controlled by onboard sensors and computing equipment. Like some of today’s advanced driving systems from the auto industry, drivers are able to relax their attention from the gas and brake pedals.

Stakeholders are enthusiastic about the safety and efficiency enhancements truck platooning makes possible. Reduced drag for follower vehicles equates to fuel savings and lower emissions. Platooning trucks take up less space on the road, which means more space for cars. And giving control of steering and braking to a tireless machine could reduce the occurrence of accidents caused by human error.

But at the TRB annual meeting, researchers were eager to discuss how truck platooning could have a potentially negative impact on one aspect of the transportation system; namely, infrastructure. And it has to do with weight.

Talk to a road, and it would say, “You think driving is stressful? Imagine how I feel. I was in pristine condition six months ago, but all this weight is making me crack under the pressure.”

States spend gobs of taxpayer money to repair and maintain roads damaged by vehicle traffic, particularly from large trucks. In Louisiana, for example, lawmakers used to require freight companies to pay a $100 tax per truck to offset the damage to state highways wrought by overloaded sugarcane hauls. Later, the state passed legislation requiring companies who wished to haul more than 100,000 tons at a time to add an additional axle to their vehicles for better weight distribution. In doing so, the state saved millions in revenue lost to road damage caused by heavy truck loads.

At TRB this year, part of the platooning discussion centered specifically on the impact of platoon weight on bridges. Truck platoons result in more big-rig poundage being concentrated in a smaller area, causing potential damage to bridge decks, beams, joints and pavement. Think of an elephant stepping on your foot. And with the American Society of Civil Engineers classifying four out of 10 U.S. bridges as being 50 years or older in 2017, with nearly 10% being rated as structurally deficient, the question of safety and financial impacts due to platooning looms large.

Platooning is anticipated to boom in the commercial freight industry in the coming years, and states are already paving the way for its widespread adoption. Michigan, for example, recently passed legislation eliminating the 500-ft gap distance previously required between trucks in order to facilitate platooning. But researchers assert that the time for heavy assessment of impending infrastructural impacts, especially bridges, is now.

“Do you break the platoon on the bridge? We need the research to [tell us],” suggested Richard Dunne, director of structures at the engineering firm Michael Baker International, while presiding over the TRB session Truck Size and Weight: What You Need to Know. “We should be looking at what 10 feet to 20 feet platoon loads look like to the bridge.”

Given the gravity of the issue, you can expect to see new research this year. How will it impact platooning legislation? And will Congress initiate the revitalization of the U.S. transportation infrastructure in 2018, which would subsequently address the issue? Guess we’ll find out in the long haul.